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Income Taxes (Details) (USD $)
6 Months Ended 12 Months Ended
Sep. 30, 2014
Mar. 31, 2014
Income Taxes    
Minimum percentage of qualifying income of non-taxable subsidiaries 90.00%ngl_MinimumPercentageOfQualifyingIncomeOfNonTaxableSubsidiaries 90.00%ngl_MinimumPercentageOfQualifyingIncomeOfNonTaxableSubsidiaries
Uncertain tax positions $ 0us-gaap_UnrecognizedTaxBenefits